The present invention relates to a method for separating a specimen and a method for analyzing the separated specimen, and particularly relates to a method for separating a minute region from the substrate of a specimen such as a semiconductor wafer, and an analysis method using the separating method.
As a conventional technique of such a separating method, there has been a technique disclosed in "Microscopy of Semiconducting Materials Conference, Oxford, (1989), pp. 501-506". In this document, there is a description about an example in which a thin film specimen analyzed through a transmission electron microscope (hereinafter abbreviated to "TEM") is cut out by use of a focused ion beam (hereinafter abbreviated to "FIB").
According to the contents of disclosure in the above document, a chip 71 having a length of several mm and a width of 100-500 .mu.m is cut out from a semiconductor integrated circuit by use of a diamond wafering saw, being fixedly mounted on a copper grid 72 (standard grid of the TEM for observing the chip), as shown in FIG. 7. Then the chip 71 is processed by the FIB to be formed into a thin film specimen 73. Then the thin film specimen 73 is irradiated with an electron beam 74, being observed by use of the TEM. In FIG. 7, the reference numeral 75 represents a rectangular opening.
As another conventional technique, there has been a technique disclosed in "Proceedings of International Reliability Physics Symposium, (1989), pp. 43-52". In this document, there is a description about an example in which a section of a device is processed by use of the FIB, and the structure of the section is observed by means of a function of a scanning ion microscope (hereinafter abbreviated to "SIM").
In conventional TEM observation, generally, a specimen is thinned by polishing, being observed. Therefore, it was impossible to set the place of observation and direction of the specimen desirably and precisely. Indeed the first-mentioned technique is a superior method in which an image of a specified portion of a specimen can be observed through the TEM. In this method, however, it is necessary to carry out a step in which a region having a length of several mm and a width of 100-500 .mu.m and including a portion to be analyzed is mechanically separated from the chip of an integrated circuit or semiconductor wafer. When a wafer is a specimen substrate, it is necessary to divide the wafer for observation. Further, it is difficult to process a specimen to have a thickness not thicker than 100 .mu.m through mechanical processing by means of a diamond wafering saw or the like from a point of view of processing accuracy and damage. Accordingly, there is a defect that the rest portions which could not be cut to be thin enough through mechanical processing is necessary to be processed with the FIB, and it takes a long time for the processing.
In the conventional observation of a section by use of the SEM, an observation specimen is cleaved, and the plane of cleavage thereof is observed. Accordingly, it is impossible to specify a desired portion precisely, and it is difficult to observe the section thereof. Indeed the above-mentioned conventional techniques have advantageous in that a section at a certain portion of a specimen can be observed. However, they have disadvantageous in that it is difficult to make a section perfectly or substantially flat and parallel to the specimen surface for observation, and it is impossible to observe, for example, a horizontal section of a contact hole.